The present invention generally relates to apparatus and methods for disengaging generators and other rotating machines from a prime mover and, more particularly, to apparatus and methods of disengaging an aircraft generator from an engine or gear box to prevent damage to the engine or gear box.
In the aerospace industry, aircraft receive electric power from generators. The generators may be coupled to the main engine or to auxiliary power units through a gear box. Known designs of generators have a generator drive shaft that includes some kind of shear section that is based on safe operational capability of the gearbox. In the event that the generator malfunctions, this shear section operates and protects the gear box from continuing to rotate under an unacceptable load from a malfunctioning generator that may have stopped rotating. For constant speed generators, the design of the shear section is not difficult—it is easy to design a shear section to meet one speed. However, with the evolution of variable frequency generators (VFG), where failure can occur over a range of speeds, it is rather difficult to design a shear section that can protect the gear box regardless of the multiple possible speeds of the generator.
It is therefore useful that some other means should be incorporated into the design of the generator that would help protect the gear box. If, for example, there is a minor fault with the generator and it is not producing any power but rather is rotating like a load on the gear box, it is desirable that the generator be de-coupled from the gear box.
It is also useful that such a protection means should not interfere with proper engagement of the generator with the gearbox irrespective of whether a generator shaft is producing load on the gearbox or alternatively when the gearbox may be producing mechanical load on the generator shaft.
In some prior-art aircraft applications pilot-controlled disengagement mechanisms have been used to release a malfunctioning generator from an engine. Some of these prior-art systems employ rotatable engagement members which disengage when their relative rotational speeds change. Rotational speed changes and consequent disengagement may be produced with a brake system that may be actuated by an aircraft pilot when malfunction of a generator is detected. See for example U.S. patent application Ser. No. 11/848,123 filed Aug. 31, 2007.
To enhance reliability and to minimize weight of such brake-activated systems, it is desirable to provide a disengagement assembly with a minimal number of parts. Additionally, it is desirable to provide such a system in which brake wear is reduced or eliminated.
As can be seen, there is a need to disengage the generator from the gear box as needed when the generator malfunctions. Furthermore, there is a need to have such a disengaging assembly that is controllable by a pilot of an aircraft when generator malfunction is detected. It is also required that the disengagement assembly is constructed with a minimal number of parts and so that brake wear is reduced or eliminated.